gst/rtp/gstrtpchannels.*: Add method to get possible channel positions.

Original commit message from CVS:
* gst/rtp/gstrtpchannels.c: (gst_rtp_channels_get_by_index):
* gst/rtp/gstrtpchannels.h:
Add method to get possible channel positions.

ChangeLog

@@ -1,3 +1,9 @@
+2008-10-28  Wim Taymans  <wim.taymans@collabora.co.uk>
+
+	* gst/rtp/gstrtpchannels.c: (gst_rtp_channels_get_by_index):
+	* gst/rtp/gstrtpchannels.h:
+	Add method to get possible channel positions.
+
 2008-10-28  Wim Taymans  <wim.taymans@collabora.co.uk>
 
 	* gst/rtp/Makefile.am:

gst/rtp/gstrtpchannels.c

@@ -110,6 +110,37 @@ gst_rtp_channels_get_by_order (gint channels, const gchar * order)
   return res;
 }
 
+/**
+ * gst_rtp_channels_get_by_index:
+ * @channels: the amount of channels
+ * @idx: the channel index to retrieve
+ *
+ * Get the allowed channel order descriptions for @channels. @idx can be used to
+ * retrieve the desired index.
+ *
+ * Returns: a #GstRTPChannelOrder at @idx, NULL when there are no valid channel
+ * orders.
+ */
+const GstRTPChannelOrder *
+gst_rtp_channels_get_by_index (gint channels, guint idx)
+{
+  gint i;
+  const GstRTPChannelOrder *res = NULL;
+
+  for (i = 0; channel_orders[i].pos; i++) {
+    if (channel_orders[i].channels != channels)
+      continue;
+
+    if (idx == 0) {
+      res = &channel_orders[i];
+      break;
+    }
+    idx--;
+  }
+  return res;
+}
+
+
 /**
  * gst_rtp_channels_create_default:
  * @channels: the amount of channels

gst/rtp/gstrtpchannels.h

@@ -181,5 +181,6 @@ const GstRTPChannelOrder *   gst_rtp_channels_get_by_pos     (gint channels,
                                                               const GstAudioChannelPosition *pos);
 const GstRTPChannelOrder *   gst_rtp_channels_get_by_order   (gint channels,
                                                               const gchar *order);
+const GstRTPChannelOrder *   gst_rtp_channels_get_by_index   (gint channels, guint idx);
 
 GstAudioChannelPosition *    gst_rtp_channels_create_default (gint channels);